Glossary
Tetrapeptide
A tetrapeptide consists of four amino acids linked by three peptide bonds. Why this length turns up in bioregulators, matrikines and cosmetic peptides.
Tetrapeptides contain precisely four amino acid residues connected through three peptide bonds. Depending on the side chains, their molecular weight usually lies between about 350 and 600 Da, which puts them comfortably under the common 500 Da rule-of-thumb limit for passive diffusion only if the residues are small and carry no charge.
Why four residues is so common
A four-residue chain is long enough to display a defined arrangement of side chains, yet short enough for standard SPPS to make it inexpensively and at high purity, with few deletion impurities and a clear-cut mass spectrum. This mix of features explains why the length crops up in fields that otherwise have nothing in common: Epitalon (Ala-Glu-Asp-Gly) among the Khavinson bioregulators, Rigin and Tetrapeptide-21 in cosmetic formulations, the matrikine fragments investigated in skin research, and Tetrapeptide-30 in pigmentation studies.
The small size has practical effects. Unless the N-terminus is capped, aminopeptidases clear tetrapeptides quickly; they typically come as acetate or TFA salts in which the counter-ion makes up a considerable share of the vial mass; and very polar sequences may absorb enough moisture to make weighing awkward.
Related terms and material
tripeptide · molecular weight (Da) · purity. Reference material: Epitalon, cosmetic signal peptides. Further reading: peptide sequences explained.